Two general categories of rigs include drilling rigs and service/workover rigs. Drilling rigs are used to drill wells (e.g., oil, natural gas), while service/workover rigs are used to service or work existing wells for any appropriate reason. Representative servicing or workovers of existing wells includes without limitation replacing one or more components (including downhole components) associated with the well (e.g., tubing, valves, seals, flanges, blowout preventers), directing one or more components into the well for any appropriate purpose (e.g., a tool for opening a downhole blockage), executing one or more well operations (e.g., fracturing, acidizing), or the like.
Both drilling and service/workover rigs typically use a derrick or mast that supports one or more pulleys, one or more block and tackles, or the like. Various lines, cable, or the like may be directed around one or more of these pulleys/block and tackles to lift the desired component(s) and/or to lower the desired component(s) as desired/required. These lines or cables are anchored to what is commonly referred to in the art as a drawworks. An appropriate power source (e.g., a right angle drive) rotates one or more drums of the drawworks in one direction to wind the line/cable around one or more drums of the drawworks to lift the desired component(s), while the power source rotates one or more drums of the drawworks in the opposite direction to unwind the line/cable from one or more drums of the drawworks to lower the desired component(s). “Cable” is commonly viewed as being of a heavier grade than “line,” and thereby more appropriate for handling heavier components. Cable is commonly associated with a main drum of a drawworks, while line is commonly associated with a sand drum of a drawworks. Service or workover rigs use a drawworks having both a main drum and a sand drum, while drilling rigs typically only use a main drum.
The mast or derrick of service/workover rigs oftentimes extends in excess of 90 feet. Many service/workover rigs are incorporated by a truck/tractor for transporting the same from location to location. Moreover, the mast is typically movable between a stowed position (e.g., at least generally horizontal, and including for transportation purposes) and a deployed position (e.g., at least generally vertical, although in practice most masts are disposed at a small angle relative to vertical). In addition to being deployable, the mast should be designed to accommodate the loads that will be experienced during operation of the service/workover rig.